System for irradiating living tissue, or simulations thereof

ABSTRACT

A system for irradiating living bodies, or portions thereof, using electromagnetic radiation (EMR). A source or generator provides electromagnetic energy at a selected frequency, within an operational band width, via a coaxial cable to an applicator for radiation into living tissue. The source, cable, and applicator each have a characteristic impedance approximately equal to the average impedance of the living tissue over a broad frequency band, thus enabling efficient operation of the apparatus without using auxiliary impedance matching devices. The applicator is of a waveguide transmission line type enabling efficient transmission and radiation of the electromagnetic energy and further incorporates means for cooling surface portions of the living tissue during radiation thereof. Selective dielectric loading of the applicator enables shaping of the radiated power to a preselected distribution. A feedback control system including temperature sensors placed onto and into the tissue enables the control of tissue surface and sub-surface temperatures within a preselected range by adjusting the power level of the generator.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.315,749, filed on Oct. 28, 1981, now abandoned, and which was a divisionof U.S. patent application Ser. No. 48,515 filed June 14, 1979, whichissued as U.S. Pat. No. 4,341,227 on July 27, 1982 and which was acontinuation-in-part of U.S. patent application Ser. No. 2,583 filedJan. 11, 1979, now abandoned.

The present invention relates generally to irradiating human or animaltissue, and more particularly to electromagnetic radiation (EMR)apparatus for such irradiation, for example, to produce hyperthermiawithin living bodies, or portions thereof.

It has been long known that electromagnetic energy at frequenciesgreater than about 10 KHz produces heating in living tissue. In fact,many years ago the word "diathermia" was used to describe the heating ofhuman tissue by high frequency electrical currents.

Such heating may have many beneficial uses, such as, for example, thewarming of selected tissue after hypothermal surgery, the enhancement ofblood circulation, and the necrosis of selected tissue such as tumorsand malignant growths.

With regard to the latter, it is generally known that death, ornecrosis, of living tissue cells occurs at temperatures elevated abovethe normal cell temperature and that the death rate of the tissue is afunction of both the temperature to which it is heated and the durationfor which the tissue is held at such temperature.

It has been reported that some types of malignant cells can apparentlybe necrotized by heating them to a temperature which is slightly belowthat temperature injurious to most normal cells. In addition, some typesof malignant cells may be selectively heated and necrotized byhyperthermia techniques because masses of these malignant cellstypically have considerably poorer blood flow heat dissipationproperties than does the surrounding normal tissue. As a result, whennormal tissue containing such malignant masses is heated by EMR, theresultant temperature of the malignant mass may be substantially abovethat of surrounding healthy cells.

Although some disagreement exists regarding exact temperatures, mostmalignant cells have a relatively limited temperature range in whichhyperthermia is effective in causing necrosis. Below a thresholdtemperature of about 41.5° C. (106.7° F.) insubstantial thermal damageoccurs even in those types of malignancies which have a greatersensitivity to temperature than do normal cells. In fact, attemperatures just below this threshold, growth of some types ofmalignancies may be stimulated. At temperatures within or above about43° to 45° C. (109.4° to 113° F.) thermal damage to most normal cellsoccurs.

Because of the normal cooling and heat transfer properties of a largebody, such as a human body, or portions thereof, deeply locatedmalignant growths can seldom be heated to a lethal temperature usingsurface heating techniques without causing excessive thermal damage tothe overlying normal tissues.

An advantage of EMR is that energy incident to a body is not totallyabsorbed by the surface tissue; rather, a substantial amount of energypenetrates some distance into the body before it is absorbed to causeheating. It is generally known that lower frequency EMR has greaterpenetration into tissue than higher frequency EMR. For example, inaccordance with an article by A. W. Guy, et al, published in Proceedingsof the IEEE, Vol. 63, No. 1, January, 1974, entitled "TherapeuticApplication of Electromagnetic Power", the depth of penetration in humanmuscle and fat at 100 MHz is 6.66 cm. (2.62 in.) and 60.4 cm (23.8 in),respectively, while at 915 MHz the depth of penetration is only 3.04 cm(1.2 in) and 17.7 cm (6.97 in) respectively.

A serious problem associated with EMR hyperthermia of a malignant growthlocated deep within a body, has been causing lethal heating of themalignancy without overheating and damaging a large amount of adjacenthealthy tissue or healthy surface tissue layers. Such overheating ofnormal cells may occur because the applicator used to radiate EMR intothe body, emits a distorted energy distribution into the tissue, theapplicator is not efficiently coupled with regard to transmission of theEMR, into the body tissue, or surface cooling is not adequate.

That is, the applicator, during EMR, causes certain areas to receivesignificantly more energy than adjacent areas and as a result such areasbecome "hot spots".

This problem is further complicated when the EMR frequency is below 1gigahertz. In general, the lower the EMR frequency, the larger theapplicator must be in order to effectively carry and radiateelectromagnetic energy into tissue and, as a result, applicators forefficiently irradiating electromagnetic energy below 1 gigahertz tend tobe large in size and cumbersome to handle. In addition, such applicatorsemit low frequency EMR in a large radiation pattern which is notsuitable for heating small masses of malignant tissue located wellbeneath surface layers of the body being irradiated.

It is well known that waveguide transmission lines can efficientlyconduct or transmit electromagnetic energy. Such waveguides, however,useful for carrying electromagnetic energy in the frequency range below1 gigahertz are also generally large and cumbersome, unless they aredielectrically loaded, or filled, with a dielectric material having adielectric constant substantially greater than unity.

Early attempts, such as, for example, disclosed by G. C. Southworth inU.S. Pat. No. 2,407,690, issued on Sept. 17, 1946, to utilize adielectrically loaded waveguide as an electromagnetic applicator in anelectrotherapeutic system, only recognize the principle of loading awaveguide to reduce the size thereof, without solving the problems ofproducing "hot spots" as hereinabove referenced. Further, suchapplicators are limited in operation to a single or limited frequencyrange and require extensive tuning apparatus. Hence, they are notsuitable for heating tissue at different depths within the body.

Although lower frequency EMR has greater penetration into a body, thesurface areas are also heated, and during extended application of EMRmay become hot enough to damage surface tissue. In order to efficientlycouple the energy radiated from the applicator into the body tissue itis necessary to position the applicator in contact with, or very closeto, the body surface. Hence, a conventional applicator placed in directcontact with surface tissue or immediately adjacent thereto interfereswith access to such surface areas to enable cooling thereof by auxiliaryapparatus.

G. Kantor, in U.S. Pat. No. 4,108,147 issued on Aug. 22, 1978 recognizedthat the coupling of electromagnetic energy into body tissue is enhancedby utilizing an applicator adapted for direct contact with tissue to beirradiated. Further, the applicator disclosed by Kantor is of adielectrically loaded waveguide type, in order to provide a more uniformheating pattern than a spaced applicator.

However, Kantor does not address the problem of efficiently couplingelectromagnetic energy from a source, into living tissue, nor theproblem of cooling surface layers thereof.

The problems of low efficiency and inflexibility of hyperthermiaapparatus are common with generally available diathermy systems. Suchapparatus has heretofore typically included arrangements of standard EMRcomponents, and as a consequence of using "off-the-shelf" components,mismatch of characteristic impedances (Z_(o)) at various interfaces andinterconnections has frequently limited EMR hyperthermia systemefficiencies.

Component mismatch has many times been ignored or been compensated forby "tuners" and "line stretchers" positioned at calculated distancesbetween an EMR generator and the mismatching interface. These devicesmay be adequate when only a single EMR frequency or a very narrow rangeof EMR frequencies is needed in the system. However, to irradiateselected tissue located at different depths within the body and overdifferent areas, capability for varying applied EMR frequencies over arange of frequencies is necessary. Further, such compensating "tuners"and "line stretchers" create standing waves within the EMR apparatuswhich results ultimately in unwanted heating of connecting cable,decreasing efficiency and increasing leakage radiation. As a result ofthese and other problems, safe, efficient and relatively simple lowfrequency (below 1 gigahertz) EMR hyperthermia apparatus have notheretofore been generally available.

The present invention provides EMR hyperthermia apparatus whichefficiently couples electromagnetic irradiation into tissue at aselected frequency, throughout a relatively broad frequency range,without the necessity of auxiliary impedance matching apparatus.Included, in the invention are highly efficient EMR applicators capableof uniformly and efficiently heating deep portions of a body using EMRfrequencies below 1 gigahertz while cooling surface portions of thebody.

A system for radiating living tissue or simulations thereof, inaccordance with the invention, comprises an electromagnetic radiationsource having an output impedance substantially equal to an averagecharacteristic impedance of a waveguide-type transmission lineapplicator adapted for radiating electromagnetic energy into the tissue.The applicator includes a dielectric disposed partially filling thetransmission line and in operative relationship therewith which enablesthe applicator characteristic impedance, when radiating into tissue tobe approximately equal to an average characteristic impedance of livingtissue or simulations thereof, at a selected frequency. Interconnectingthe applicator and the electromagnetic radiation source are transmissionmeans having a characteristic impedance substantially equal to theaverage characteristic impedance at the selected frequency.

Since the electromagnetic radiation source, the applicator and thetransmission means all have approximately the same characteristicimpedance and these characteristic impedances are approximately equal tothe average characteristic impedance of the living tissue, substantiallyno reflection of EMR occurs at interfaces therebetween, because ofimpedance mismatch, and as a consequence the apparatus efficientlycouples electromagnetic radiation from the source into the body withoutappreciable energy loss.

In an exemplary embodiment of the invention, the radiation source is ofa variable frequency type and has an output impedance substantiallyequal to an average characteristic impedance of tissue, or simulationsthereof over a selected frequency range having a band width ratio inexcess of 50%.

A dielectric medium, in operative relationship with the waveguide-typetransmission line, enables the applicator to have a characteristicimpedance, when radiating into the tissue approximately equal to theaverage characteristic impedance throughout the recommended frequencyrange. Hence the apparatus is able to efficiently couple EMR into tissueat any frequency within the applicator's band width without the need forauxiliary apparatus, such as "stub tuners" which would requireadjustment upon changing from one frequency to another.

By incorporating cooling means within the applicator the apparatus cancool surface areas despite the fact that the applicator is placed incontact with or adjacent to the tissue for efficient energy couplingthereinto.

A feedback control system, in operative relationship with theelectromagnetic radiation source and including at least one temperaturesensor disposed in said living tissue, or simulation thereof, acts tolimit the temperature of monitored portions of the living tissue bycontrolling the output of the radiation source.

Additionally, the invention includes waveguide-type applicators for usein the system, or separately, which include a waveguide-typetransmission line, dielectric means partially filling the transmissionline, and disposed in operative relationship therewith for enabling thetransmission line to have a characteristic impedance, when radiatingelectromagnetic energy into the tissue, approximately equal to anaverage characteristic impedance of the living tissue, or simulationsthereof, at a selected frequency, and coupling means adapted forreceiving electromagnetic energy from a conductor and for launching theelectromagnetic energy into the waveguide-type transmission means.

In one embodiment of the invention an applicator includes a generallyrectangular waveguide-type transmission line having sidewalls withinterconnecting top and bottom portions. The dielectric is disposedwithin the transmission line and along the sidewalls thereof and, inaddition to enabling the applicator to have a preselected characteristicimpedance, it also causes the transmission line to irradiateelectromagnetic energy in a preselected energy distribution into livingtissue.

A coupler is included for receiving electromagnetic energy from acoaxial-type conductor and for launching the electromagnetic energy intothe waveguide transmission line. The coupler has portions thereof whichare disposed within the transmission line and in operative relation withthe dielectric for launching the electromagnetic energy into thetransmission line without substantial electromagnetic energy reflectedinto the coaxial conductor. These features further enables the use ofthe applicator with a coaxial cable without energy loss in the form ofelectromagnetic energy reflections along the coaxial conductor and backinto the radiation source which may either damage the source, result inundue heating of the coaxial conductor, or cause radiation leakage whichmay be hazardous to operating personnel.

A blower is incorporated into the applicator for forcing cooling airthrough an air passage through the dielectric and out an electromagneticenergy radiating end of the transmission line. Since the applicator ispositioned adjacent the surface of the tissue during radiation oftissue, air emitted from the transmission line flows across the surfaceportions of the living tissue to cause cooling thereof.

In another embodiment of the invention an applicator includes awaveguide-type transmission line having a central portion and adjoiningopen side portions with the dielectric being disposed within the centralportion of the transmission line.

A further embodiment of the invention, includes an applicator forirradiating electromagnetic energy into living tissue, or simulationsthereof, having a waveguide-type transmission line, first dielectricmeans, and second dielectric means. The first and second dielectricmeans are disposed in operative relationship with the transmission linefor enabling the transmission line to have a characteristic impedance,when radiating electromagnetic energy into the tissue, approximatelyequal to an average characteristic impedance of the living tissue, orsimulations thereof, at a selected frequency.

Coupling means are provided for receiving electromagnetic energy from acoaxial type conductor and for launching the electromagnetic energy intothe waveguide-type transmission line without substantial electromagneticenergy reflection into the coaxial conductor throughout said frequencyrange.

In addition, the second dielectric means includes a fluid dielectric anda compartment for containing the fluid, said compartment being disposedwithin the transmission line adjacent one end thereof. The compartmentincludes a wall forming an applicator radiating surface and fluid inletand outlet means for enabling the fluid dielectric to be circulatedthrough the compartment, thereby enabling the second dielectric means toact as a cooling medium for cooling surface portions of living tissueduring irradiation thereof by the applicator when the tissue is heldagainst the applicator radiating surface.

Other advantages and features of the invention will appear from thefollowing description when considered in connection with theaccompanying drawings, in which:

FIG. 1 is a representation, partially in perspective and partially inblock diagram form, of an exemplary embodiment of a system forirradiating living tissue, or simulations thereof and generally showinga waveguide-type transmission line applicator, electromagnetic energysource, a coaxial cable for transmitting electromagnetic energytherebetween, and a feedback system which includes temperature sensors,a controller and a record/display module;

FIG. 2 is an enlarged perspective view of the waveguide-typetransmission line applicator, partially broken away to show dielectriccompartments within the waveguide, a ribbed filler therebetween, and acoupler for receiving electromagnetic energy from the cable and forlaunching received electromagnetic energy into the waveguide;

FIG. 3 is an overall perspective view of the waveguide-type transmissionline applicator showing an EMR emitting end, or face thereon and an endsurface of the ribbed filler;

FIG. 4 is a cutaway plan view of the applicator of FIG. 3, showing thedisposition of dielectric within the waveguide, the position of thecoupler with respect to the dielectric and waveguide, and a blowerdisposed on a rear end of the wave guide applicator for forcing airtherethrough to cool surface areas of tissue when the waveguideapplicator is positioned in operative relationship therewith; also shownis a representation of a temperature sensor disposed at a surfaceposition on the tissue sample and a representation of air flow throughthe applicator and over the tissue sample;

FIG. 5 is a plot of a temperature distribution or heating pattern at thesurface of a simulated tissue sample after irradiation thereof with theapplicator shown in FIG. 3; an outline of emitting end of the applicatoris indicated to show the relative shape of the heating pattern withrespect thereto;

FIG. 6 is an overall perspective view of another embodiment of awaveguide-type transmission line applicator partially broken away toshow the dielectric therein, and a coupler for receiving electromagneticenergy from a coaxial cable and for launching the receivedelectromagnetic energy into the waveguide applicator;

FIG. 7 is a cutaway plan view of the applicator of FIG. 6 showing thedisposition of dielectric therein and the position of the coupler alongwith a representation of air flow through the applicator and across thesurface of tissue being irradiated; also shown is a representation of atemperature sensor disposed at a surface position on the tissue sample;

FIG. 8 is a cross sectional view taken along line 8--8 of FIG. 7 showingin greater detail the configuration of the waveguide shape and thecoupler therein;

FIG. 9 is an overall perspective view of an alternative embodiment ofthe applicator shown in FIG. 6 in which a top portion of the applicatorof FIG. 6 is electrically represented by a metal flap, in order that theover-all size of the waveguide applicator may be reduced whilemaintaining approximately the same size radiating area of the applicatorshown in FIG. 6; and,

FIG. 10 is a plot of a temperature distribution or heating pattern justunder the surface of a simulated tissue sample after irradiation thereofwith the applicator shown in FIG. 9; the outline of a radiating end offace of the applicator is indicated to show the relative shape of theheating portion with respect thereto;

FIG. 11 is an overall perspective view of another embodiment of awaveguide-type transmission line applicator similar to the applicator ofFIG. 6 which includes a compartment within the waveguide for containinga second fluid dielectric which may be circulated through thecompartment to provide a cooling medium for cooling surface portions oftissue held against the applicator, the second dielectric additionallyproviding electromagnetic beam collimation, the applicator beingpartially broken away to show the disposition of a first dielectrictherein;

FIG. 12 is a cross sectional view of the applicator of FIG. 11 takenalong line 12--12 showing the disposition of a coupler and thedielectrics therein;

FIG. 13 is a diagram of electromagnetic energy radiated from a radiatingsurface showing the relative divergence of electromagnetic energy withinnear and far field areas from said radiating surface;

FIG. 14 is a plot of a temperature distribution or heating patternapproximately one centimeter below the surface of a simulated tissuesample after irradiation thereof with the applicator shown in FIG. 11,the outline of a radiating end of face of the applicator is indicated toshow the relative shape of the heating portion with respect thereto;and,

FIG. 15 is a plot of a temperature distribution or heating patternapproximately four centimeters below the surface of a simulated tissuesample after irradiation thereof with the applicator shown in FIG. 11,the outline of a radiating end of face of the applicator is indicated toshow the relative shape of the heating portion with respect thereto.

Referring now to FIG. 1, a system 10 for irradiating living tissue 12 orsimulations thereof, including a malignant mass 14, generally includesan electromagnetic radiation generator or source 18, an applicator 20and a coaxial cable 22 for transmitting electromagnetic energy betweenthe source and the applicator. It should be appreciated that a waveguidetype transmission line could be employed to conduct electromagneticenergy between the source 18 and the applicator 20, however, the coaxialcable is preferred because it permits greater flexibility in movement ofthe applicator.

In order to control or hold the temperature of the irradiated tissue 12,the malignant mass 14 and surface portions, or layers, 24 of the tissue,within a preselected range, the system 10 includes a feedback controlsystem 28 including temperature sensors 34, 36, 38, a controller 40 andan input/record/display module 42. Hereinafter, reference may be madeonly to tissue, however, it should be understood that such reference ismeant to include both living tissue and simulations thereof.

In operation, the applicator 20 is held immediately adjacent the tissuesurface 12 by a bracket 48 and a supporting arm 50. Electromagneticenergy is fed from the source 18 via the cable 22 into the applicator 20and thereafter radiated into the tissue, as indicated by the arrows 52,towards the malignant mass 14 located within the tissue.

It is important that the applicator be placed in contact with, orimmediately adjacent to the tissue to be irradiated in order to achieveproper coupling of the radiated energy thereinto. At frequenciesapproaching 1 gigahertz, a significant amount of energy may be absorbedby the tissue surface 24 causing heating thereof to a temperatureexceeding 43° C. unless otherwise cooled.

A feature of the present system 10 is that the applicator 20 includesmeans for cooling of the surface tissue 24 during radiation thereof,using forced air or liquid, and importantly directing such cooling ontothe irradiated area.

As will be discussed hereinafter in greater particularity, theapplicator generally includes a blower 58 for forcing air through theapplicator and across the surface portions as represented by the arrows62, indicating inlet air, and arrows 64, indicating the outlet airflowing over the tissue surface 24.

The temperature sensor shown at 34 is representative of one or aplurality of sensors disposed at or just below the surface layer 24, asingle sensor being shown for clarity. Similarly, the sensors shown at36 and 38 respectively represent one or a plurality of sensors disposedin, and adjacent to, respectively, the malignant mass 14.

It is to be appreciated that such sensors should be of a type which doesnot interfere or absorb electromagnetic energy, otherwise correct tissuetemperatures will not be ascertained. Such sensors may be of athermister type utilizing carbon-impregnated plastic leads, optical typewith connecting optical fibers, or a liquid crystal type as generallydescribed by Cetas, T. C. in PROCEEDINGS OF THE INTERNATION CONFERENCEON CANCER THERAPY, HYPERTHERMIA AND RADIATION, Apr. 28-30, 1975,Washington, D.C. (Am. Coll. of Radiology, Chevy Chase, Md.).

The temperature sensors 34, 36, 38 are connected to the controller 40via lines 72, 74, 76 respectively, connected to sensor lead portions 78,80, 82 which are sufficiently long enough to extend beyond the radiationfield 52 of the applicator. Such leads are customarily provided with thetemperature sensors.

The controller 40 includes computing portions, not shown, for receivingsignals from the temperature sensors 34, 36, 38 and comparing suchsignals with predetermined signals corresponding to preselected or settemperature levels as inputed to the controller 40 via module 42 througha connecting line 88. The controller 40 may operate in a comparator likemanner to control the output of the source 18 to the applicator 40 viathe interconnecting line 90. For example, when the temperature of any ofthe temperature sensors 34, 36, 38 reaches a set temperature level, thecontroller will act to either reduce the power output of the source 18,or shut it off entirely, until the temperature, as indicated by thesensors, falls below the set temperature level.

The module 42 may include recording and output facilities, such as aprinter/plotter and CRT monitor, not shown, so that the entiretime-temperature relationship of the tissue 12 as indicated by thesensors 34, 36, 38, can be monitored during irradiation.

It is important to note that the system 10 does not require impedancematching devices, such as "stub tuners" or "line stretchers" to operateefficiently. However, such a tuner would provide some small improvementin efficiency and reduction in reflected power. The source 18, cable 22and applicator 20 each have a characteristic impedance substantiallyequal to the average characteristic impedance of the tissue over therange of frequency to be radiated into the tissue. Hence, there beinglittle impedance mismatch, efficient conveyance of electromagneticenergy is possible without auxiliary matching devices. However, sincedifferent bodies have various fat layers and moisture content, a tuningdevice would still further increase efficiency and reduce reflectedpower.

More specifically, for animal tissue 12, the average characteristicimpedance is, in part, a function of (1) the frequency of theelectromagnetic field set up therein, (2) the specific content of thetissue, namely, bone, fat, or muscle; and (3) the temperature of thetissue. For the frequency range between 50 megahertz and 1 gigahertz, anoverall average real impedance of animal tissue is approximately 50ohms.

As will be hereinafter discussed in further detail, the characteristicimpedance of the applicator 20, when radiating into animal tissue 12,over a frequency range between approximately 420 to 750 MHz, is close to50 ohms. The coaxial cable 22 is of a common commercial type having acharacteristic impedance of 50 ohms as is the electromagnetic radiationsource 18. The source may be of a single frequency type, however, forgreater flexibility in experimentation and in varying the depth ofpenetration of the electromagnetic energy, a variable frequency sourceis preferred, such as a model 15152 RF power generator manufactured byMCL Inc. (Microwave Components Laboratory), which has a frequency rangeof 10 megahertz to 2500 megahertz and an output power of approximately100 watts, with various plug-ins.

Referring now to FIG. 2, the applicator 20 for use with the radiationapparatus 10 includes a generally retangular waveguide-type transmissionline 96 having a top and bottom 98, 100 with inner connecting sidewalls102, 104. The top, bottom and sidewalls of the waveguide 96 are formedof sheet metal material having flanges 110 thereon suitable for bondingto adjacent top, bottom or sidewall portions by means of welding, orother means, not shown, to form a generally rectangular waveguide 96having general overall dimensions of approximately eight (8) inches inlength, six and two thirds (62/3) inches in width and four (4) inches inheight.

The waveguide-type structure of the applicator permits more efficienttransfer of electromagnetic energy therethrough than many other types ofapplicators hereinbefore used, such as parabolic reflectors, paddles orthe like, over a wide operational bandwidth.

In general, the overall dimensions of the waveguide-type transmissionline are dependent upon the frequency of the energy to be radiatedthereby. The applicator 20 is representative of a class of applicatorswhich may be constructed in which an applicator designed for higherfrequencies would be proportionately smaller and one designed for lowerfrequencies would be proportionately larger than the applicator 20,which has an operational range of between 420 MHz and 750 MHz.Determination of the applicator dimensions is generally experimentalusing certain theoretical guidelines as will be presented in a latersection.

To provide a shaped energy distribution across an EMR emitting end orface 112, see also FIG. 3, the waveguide-type transmission line 96 isdielectrically loaded along the sidewalls 102, 104 thereof. As will behenceforth discussed, this dielectric loading also enables theapplicator to be smaller in dimensions than a totally air filledwaveguide, and in part enables the applicator to have a characteristicimpedance approximately equal to 50 ohms over the frequency of 420-750MHz.

In the way of definition, "dielectric loading" means the use of adielectric medium in or about a waveguide which alters the electricfield therein. A dielectric medium is a non-conducting material havingthe property that the energy required to establish an electric fieldtherein is recoverable, in whole or in part as electric energy. Forreference purposes the dielectric constant of air is 1.0.

The dielectric loading in the applicator 20 includes two generallyrectangular sidewalls or compartments 114, 116 having thin walls 118,120 (see also FIG. 4) of a relatively low dielectric constant materialsuch as plexiglass, which are filled with a dielectric medium 122 havinga relatively high dielectric constant of approximately 12. As shown, thedielectrically loaded compartments 114, 116 extend between the waveguidetop 98 and bottom 100 from the emitting end 112 to a predetermineddistance d, from a waveguide rearward end 126. As will be hereinafterdiscussed, the placement of the dielectrically loaded compartmentswithin the waveguide 96 enhances the operational frequency bandwidth ofthe applicator 20.

While the dielectric medium may be in any form, in this instance thedielectric medium 122 is a powder known as Eccoflex HiK adjusteddielectric pack-in-place powder available from Emerson & Cummings, Inc.

Use of the dielectric medium as disposed within the waveguide 96,permits the applicator 20 to conduct electromagnetic energy in thefrequency range of 420-750 MHz in a relatively small waveguide, namely62/3 inches by 4 inches. For comparative purposes, if a waveguideapplicator were constructed without dielectric loading, to efficientlyconduct electromagnetic energy in the approximate 420-750 megahertzrange, the dimensions of the waveguide would necessarily beapproximately 35 inches by 20 inches according to conventionalwaveguide-type transmission line design. Clearly, an applicator havingdimensions of this magnitude would be inappropriate for use inselectively heating portions of living tissue within most bodies. Hence,it can be seen that the dielectric loading permits the applicator toconduct electromagnetic energy in this frequency range while maintaininga usable radiating face 112 of approximately four (4) inches by a sixand two-thirds (62/3) inches.

The dielectric filled compartments 114, 116 are supported and held in aspaced apart relationship by a low dielectric filler 130 having a set ofspaced apart ribs 132 formed therein. Formed of a low dielectric(approximately 1.2) foam material, also available from Emerson &Cummings, Inc., the filler acts electrically as air. If another form ofdielectric medium or manner of constructing the compartments isemployed, the filler 130 may be modified or eliminated altogether.

It is important, however, that the central portion of the waveguide 96be air filled, or with a medium having a dielectric constantapproximately equal to air in order that the applicator emits energy ina preselected shaped distribution. The exact dimensions of thecompartments 114, 116 and the filler 130 therebetween are foundexperimentally using theoretical guidelines as will be presented in alater section.

Additionally, it is important that the filler 130, or space between thecompartments, be open if air cooling of the surface tissue 24 isprovided. It is to be appreciated that if liquid cooling is used thefiller 130 may not be open to the flow of air.

As previously discussed, the higher the radiation frequency, the lesspenetration of the electromagnetic energy into tissue. In other words, agreater proportion of the energy is deposited at or near the surfacelayers of the tissue. Consequently for the applicator 20 operating atthe higher end of its range, namely near 750 MHz, it is an importantfeature that the surface layers of the tissue can be cooled to preventoverheating and hence, unwanted necrosis of skin or surface tissue.

As shown in FIGS. 2 and 4, the air blower 58 is mounted to a mountingplate 138 attached to the rearward end 126 applicator which includes anelectrical motor 140 for driving a fan blade 142. In operation, air isdrawn in through inlet ports 148 and forced through the ribbed filler130 of the applicator. The air flow, as indicated by the arrows 64,passes over surface portions 24 of the tissue 12 causing cooling thereofby convection.

It should be appreciated that while room temperature air may be used forcooling, refrigeration coils, or a remote air cooler, not shown, couldbe incorporated to provide colder air. In addition, fluid cooling meansutilizing for example, non-metallic tubes or a liquid bag not shown, topass a dielectric cooling fluid onto or over the surface portions 24 ofthe tissue 12 may be incorporated into the applicator 20 to provide agreater cooling capacity. In fact, when the applicator 20 is positionedin contact with the surface 24, fluid cooling would be preferred overair cooling.

Referring again to FIGS. 2 and 3, the applicator 20 includes a launcheror coupler 156 for receiving electromagnetic energy from the coaxialconductor 22, not shown in FIG. 2 or 3, and for launching theelectromagnetic energy into the transmission line applicator 20. Thecoupler 156 includes a standard coaxial connector 158 having an outerthreaded portion 160 adapted for connection to the coaxial conductor 22,and a base portion 162, slidably mounted in a slot 166 in the waveguidetop 98. This mounting arrangement allows factory adjustment of thecoupler 156 within the applicator 20 in order to maximize couplingbetween the cable 22 and the applicator and substantially eliminateenergy reflection into the cable. It should be appreciated that once theoptimum position of the coupler 156 is determined, as will behereinafter discussed, the coupler position is no longer adjusted.

A center conductor 168 of the coaxial connector is connected to a rod ortube 170 having a flared or cone-like portion 172 with a flat closed end174. The cone portion of the coupler 156 and a flat end 174 thereonprovides proper capacitance coupling between the center conductor or pin168 and the waveguide 96 as is well known in the art.

The placement of the coupler 156 with respect to the dielectriccompartments 114, 116 and an unloaded or empty portion 178 of thewaveguide extending rearward from the compartments 114, 116, enables theoperational frequency band width of the applicator to be fromapproximately 420 to 750 MHz, or a bandwidth ratio of about 60%.Bandwidth ratio is defined herein to mean the ratio of ##EQU1## where f₁and f₂ are the lower and upper frequency limits respectively.

A bandwidth in excess of 30% is preferred because it enables theapparatus 10 to vary the depth of penetration of the EMR into the tissue12 as may be necessary depending on the location of the malignant mass14. This bandwidth is large compared with the operational bandwidth ofconventional dielectrically loaded waveguide applicators. Ordinarydielectrically loaded waveguide techniques would suggest the dielectricextend the entire length of the waveguide and the waveguide isterminated with a shorting plate across the side walls and top andbottom of the waveguide. The shorting plate is usually placedone-quarter wave length away from the launcher, which causes thewaveguide to have only about 20 to 30% operational bandwidth ratio, butinstead, in accordance with the technique shown by the presentinvention, dielectric load ends near the coupler 156, causing an airfilled section 178 of waveguide 96. This forces energy in the dielectricfilled portion because the air filled portion would be in cut off at thefrequencies of operation. This is inherently broad band because there isno frequency dependent quarter-wave spacing as needed when a short isused.

The location of the coupler 156, the overall dimensions of theapplicator 20 and the placement of the dielectrically loadedcompartments 114, 116 therein are determined experimentally as follows:

The length of the dielectrically loaded compartments 114, 116 should belong enough to clearly establish wave propagation therein, of theelectromagnetic energy at a frequency of interest. Since lowerfrequencies have longer wavelengths, the lowest frequency that thewaveguide applicator is to be used for is used to determine thecompartment length, L.

To establish wave propagation, the length, L, of the compartments 114,116 should be greater than approximately 1/3 of the wavelength of theelectromagnetic energy within the applicator. This wavelength is foundexperimentally by utilizing a waveguide structure, not shown, having thesame height and width of the applicator 20 but with extended side wallshaving dielectric loaded compartments extending the entire lengththereof. Electromagnetic energy at 420 MHz is fed into the waveguidestructure and the wavelength is measured. At 420 MHz, the measured wavelength is approximately 15 inches, hence the length, L, of thecompartments should be approximately 5 inches.

The distance, d, between the compartments 114, 116 and the applicatorrearward end 126 is also experimentally determined. Using a waveguidestructure, not shown, having five inch long dielectrically loadedcompartments and waveguide sidewalls of greater length, a shortingplate, not shown, extending between the sidewalls and the top and bottomof the waveguide structure, is moved toward the compartments while thewaveguide is fed by a swept frequency of 100 to 1000 MHz electromagneticenergy and the coupling efficiency is measured between the transmissionline and the feeding coaxial line by monitoring reflected power meter.The shorting plate is moved toward the compartment until reflected poweris noted to slightly change. This position of the shorting plateindicates the point at which the waveguide can be terminated withoutaffecting coupling efficiency. This distance, d, for the applicator 20is approximately 3 inches, and hence, an overall length of theapplicator of approximately 8 inches.

It should be appreciated that the rear wall 138 of the applicator doesnot act as a shorting plate or significantly afffect the coupling andelectrical operation of the application 20, but merely serves as amounting plate for the blower 58, and reduces stray radiation.

The exact location of the coupler 156 is also determined in anexperimental manner by adjusting its position within the slot 166 whilemeasuring the coupling efficiency between the electromagnetic energysource, the coaxial cable and the applicator. The coupling efficiency isdetermined in a standard manner by measuring the reflected energy fromthe applicator back towards the source while moving or tuning thecoupler 156. The optimum position of the coupler is established when theapplicator does not reflect a substantial amount of energy back towardthe source via the cable 22. In this manner, the placement of thecoupler 156 compensates for any impedance mismatch which may otherwisebe caused by the 50 ohms cable 22 being connected to the waveguide. Thisadjustment is best made while radiating the tissue, and sweeping thefrequency.

In operation, the electromagnetic energy in the frequency range ofapproximately 420 MHz to 750 MHz will be launched into the applicator bythe coupler 156 and substantially all of the energy will be conducted bythe dielectric filled portion of the guide. Little if any will pass inthe direction of the rearward air filled portion 178 to the guide.

Another important aspect of the dielectric compartments 114, 116 is thatthey are operative with waveguide 96 to shape the electromagnetic energyradiation pattern from the applicator's emitting end 112 (FIG. 3) into apreselected energy distribution.

To obtain uniformity of the electromagnetic field within the air filledor ribbed filler 130, the thickness of the side wall compartments, t,(FIG. 4), is found in accordance with the formula: ##EQU2## as discussedby Heren and Baird in IEEE Transactions of Microwave Theory andTechniques page 884-885, November 1971.

Using a frequency, f_(p), equal to approximately 420 megahertz, adielectric constant, k, of 12, and the velocity of light in free spaceC_(o), the thickness t is approximately 1.9 inches. The overall heightand width of the applicator are adjusted experimentally to cause thecharacteristic impedance of the applicator to be approximately 50 overthe entire operational range of 420 MHz to 750 MHz.

The use of dielectric compartments 114, 116 adjoining the side walls102, 104 of the waveguide 96 causes the electromagnetic energy radiationfrom the applicator emitting face 112 to be relatively less from aforward end 182 of the filler 130 than from adjoining areas 184, 186 onthe applicator emitting face 112.

The shaping of the energy distribution emitted by the applicator isparticularly important within the operational frequency range of 420-750MHz where the depth of penetration into tissue may only be a few inchesand substantial amount of energy is absorbed at or near the surfacelayers. Because the tissue being irradiated generally has uniformcooling capability, by means of blood flow, there is a tendency for ahot spot to develop in a central region of tissue being irradiated by anapplicator at these frequencies.

FIG. 5 illustrates the general shape of the heating pattern insimulated, or phantom, tissue sample for the applicator 20 whileirradiating electromagnetic energy at the frequency of approximately 420MHz, without cooling of the surface. Plotted is the percent temperaturechange near the surface relative to the greatest temperature changeindicated as one hundred percent. Actual temperature measurements weretaken at 0.6 cm. below the surface. Isothermal lines are drawn forsurface temperatures being 80 percent of the maximum temperature change,50 percent of the maximum temperature change and 44 percent of themaximum temperature change. The overall height and width of theapplicator emitting face 112 as indicated by a broken line 188.

The simulated tissue has a dielectric constant of approximately 50 ohmsover the frequency range of interest and is composed of approximately75.4% water, 0.9 NaCL, 15.2% polyethylene powder and 8.5% Superstuff.The Superstuff is a material available from WHAMO Manufacturing Co. Asshown, the heating pattern resulted from radiating the simulated tissuewith approximately 50 watts of electromagnetic energy for less than 20minutes.

Thus, the side loaded waveguide-type applicator 20 enables more energyto be coupled into tissue at 420-750 MHz beneath the emitting face 112without heating central portions of surface layers to a lethaltemperature as would otherwise be caused by uniform energy field.

This shaped emitted energy in combination with the central cooling airforced through the applicator enhances the capability of the applicatorin heating portions of the tissue, such as malignant masses, locatedbelow surface tissue, to lethal temperatures without excessive heatingof surface layers than was heretofore possible.

Additionally, the waveguide structure of the applicator 20 is moreefficient in carrying electromagnetic energy and coupling the energyinto tissue than applicators heretofore available, such as coil,parabolic reflector or paddle type applicators. The applicator 20operates within its frequency range with an overall efficiency ofapproximately 98%. That is, if 100 watts of power is applied to theapplicator at the connector 158, only two watts are "lost" from theapplicator itself, when it is properly coupled to tissue.

Turning now to FIG. 6, there is shown an alternate embodiment of awaveguide-type transmission line applicator 190 for use with theapparatus 10 for irradiating living tissue, or simulations thereof inthe frequency range of 200 to 550 MHz. In FIG. 6 like referencenumericals identify like components of the applicator 20 shown in FIGS.2, 3 and 4. Having a lower frequency range than the heretofore discussedapplicator 20, the applicator 190 enables deeper penetration ofelectromagnetic energy, and hence, deeper heating of tissue, orsimulations thereof.

In general, the applicator 190 may be classified as a ridgedwaveguide-type transmission line, and includes a waveguide 192 having acentral portion, or channel, 194 and adjoining side portions, orchannels, 196, 198. In cross section, the central and side channels 194,196, 198 form an "H" shape (FIG. 7). The channels, as well as top andbottom panels 200, 202, are constructed of sheet metal, bonded togetherby soldering, or other fastening means, not shown. Sheet metal plates204, 206 on an emitting end 208 of the waveguide join the side channelsand the central channel. The waveguide central channel 194 is filledwith a dielectric medium 122 having a dielectric constant ofapproximately 12, such as the powder described in connection with theside loaded applicator 20. It is important that the dielectric mediumfills the waveguide from the emitting end 208 to a predetermineddistance d₁, from a rear end 210' of the waveguide. As was discussed inconnection with the side wall loaded applicator 20, the dielectricmedium, in partially filling the waveguide length, in part enables thewaveguide to have a characteristic impedance over a wide frequencyrange. The ridged waveguide applicator 190 has an operational frequencyrange of 200 to 550 MHz; the frequency band width ratio beingapproximately 106%. For the applicator 190, the distance d₁, between thedielectric 122 and the rear end 210 may be approximately 3 inches whenthe overall length of the applicator 190 is approximately 8 inches orgreater; the distance, d₁, and the length, as well as the height andwidth of the applicator 190, being determined experimentally using theprocedures discussed in connection with the applicator 20.

In addition, it is important to recognize that by loading the centralportion 194 of the waveguide with a dielectric medium, essentially allof the electromagnetic energy is transmitted through the dielectricmedium, and not through the outer portions 196, 198 of the waveguide.This was pointed out in an article by Gottfried Magerl in IEEETransactions of Microwave Theory and Techniques, Volume MTT-26, No. 6,June, 1978 entitled "Ridged Waveguides Within HomogeneousDielectric-Slab Loading". Hence, although the overall height and theoverall width of the applicator are approximately 4 inches and 5.2inches respectively, the radiating portion of an emitting face 211 isessentially the height and width of the central portion 194, which areapproximately 1.4 and 3.0 inches respectively.

Referring to FIGS. 6, 7 and 8, a coupler, or launcher, 212, including acoaxial type connector 158 mounted to a top plate 214 of the centralportion 192 by means of the connector base 162 provides means forreceiving electromagnetic energy from the cable 22 and launching suchenergy into the waveguide applicator. A slot 218 in the top plate 214enables adjustment of the coupler 212 for optimizing the position of thecoupler within the ridged waveguide applicator 190 in accordance withthe procedure discussed in connection with the side wall loadedapplicator 20. An opening 216 is provided in the top panel 200 tofacilitate movement of the coupler 210 within the slot 218.

The coaxial connector center portion 168, not shown in FIGS. 6, 7 and 8,is extended by a rod or pin 220 into the dielectric medium 122. In orderto provide proper capacity coupling between the launcher 210 and thewaveguide, a T-bar section 222 is attached to the end of the pin 220. Asis well known in the art, the exact size and configuration of the pinand T-bar is adjusted to provide proper capacitance coupling being thepin and the waveguide. Other configurations and shapes of couples may beemployed with success, but as with the side loaded applicator 20, it isimportant that the relative placement of the launcher with respect tothe dielectric medium 122, and an open portion 228 of the waveguidechannel 192, is determined in a manner similar to that discussed inconnection with the side loaded applicator 20, to enable the waveguideapplicator 190 to operate over a broad frequency range, and at the sametime, enable the waveguide to have an average characteristic impedancesubstantially equal to that of living tissue, or simulations thereof,over the frequency range of 200-550 MHz.

Although the lower operational frequency range of the ridged applicator190 enables deeper penetration of the electromagnetic energy and theheating of tissue at lower levels, and proportionately less surfaceheating, cooling of surface tissue may be provided by forcing airthrough the side portions 194, 196 and across the surface portions ofthe radiated tissue 12 (FIG. 7). It is to be appreciated that, asdiscussed in connection with the side loaded applicator 20, othercooling apparatus such as tubing and fluids could be incorporated intothe side portions 194, 196 of the applicator 190 as long as suchadditional apparatus is constructed of materials which have a lowdielectric constant and hence would not interfere with theelectromagnetic field. For example, a dielectric fluid could becirculated through a dielectric container, such as a bag, not shown,which is placed in the surface of the tissue. In operation, theapplicator may be placed in direct contact with the tissue, and theplates 204, 206 may be covered with a dielectric medium 232 to bettercouple the electromagnetic energy from the applicator into the tissue 12and to prevent hot spots. Such medium may be solid or fluid, such aswater, contained in a pliable plastic bag or the like.

Referring now to FIG. 9, there is shown another embodiment of a ridgedwaveguide transmission line applicator 240 similar to the applicator190, except portions above the center channel 192 have been removed toreduce the overall height of applicator 240. In FIG. 9, like referencenumerals identify like components of the applicator 190 shown in FIGS.6, 7, and 8. The applicator 240 has open side channels 242, 244 and acentral channel 246 similar to applicator 190 with the manner ofconstruction being the same. A central channel top plate 250 extendsbetween the outer walls 252, 254 of the side channels. A dielectricmedium fills the central portion, as hereinbefore described inconnection with applicator 190, and a launcher is placed therein inaccordance with the launcher in the applicator 190. All dimensions anddetails of the dielectric medium, and launcher are substantially thesame as those discussed in connection with the applicator 190, but thefrequency range is higher. To operate in the 200 to 250 MHz range, thedimensions would change to an overall height and width of 6 inches and7.7 inches respectively, with height and width of radiating portion of 2and 4.6 inches respectively.

The upper metal face plate 204 of applicator 190 is replaced by a metalflap 260, for providing an electric simulation of the top portion of thewaveguide illustrated as applicator 190. The metal flap may be flexibleand covered with dielectric medium 262 to enhance coupling, and byattaching the flap 260 to the top 250 by means of a hinge 264, the flapmay be moved and bent so as to conform to various body shapes. Thisenhances the coupling of the EMR into the body and improves theefficiency of transfer of energy into the body tissue.

In operation, the waveguide 240 performs essentially in the same mannerand in the same frequency range as the applicator 190.

The effectiveness of the applicator 190 in causing heating in asimulated, or phantom, tissue by radiating electromagnetic energythereinto of approximately 400 MHz is shown in FIG. 10. Plotted are aset of isotherms showing the percent change relative to the greatesttemperature change of 100 percent of an area irradiated at 50 watts fora period of less than 20 minutes without surface cooling. Temperatureswere measured at a depth of 0.6 cm. below the surface. Shown areisothermal lines for 100 percent, 90 percent, 56 percent, 41 percent and27 percent of the maximum temperature achieved. Superimposed on the plotis an outline 266 of the central channel of the applicator which hasdimensions of approximately 2 by 5 inches.

Turning now to FIG. 11, there is shown still another embodiment of awaveguide type transmission line applicator 300 for use with theapparatus 10, or separately, for irradiating living tissue, orsimulations thereof, in a frequency range of approximately 200 to 800MHz. In FIG. 11, like reference of numerals identify like components ofthe applicator 190, shown in FIGS. 6, 7 and 8.

The applicator 300 of FIG. 11, is similar to the applicator 190 havingapproximately the same overall dimensions and including a waveguide 302with a central portion, or channel 304, and adjoining side portions, orchannels, 306.

As more clearly shown in FIG. 12, the waveguide central channel 304extends from a predetermined distance, d₂, from a rear end 310 of thewaveguide 302 to a compartment 312 disposed within the waveguide at aforward end 314 thereof.

The channel 304 is filled with a first dielectric medium 122 having adielectric constant of 12, such as the powder described in connectionwith the side loaded applicator 20. The channel 304 adjoins a back plate316 of the compartment 312 which consists of a low dielectric material,such as Plexiglas, which may be sealed to the waveguide 302 with anappropriate glue, or caulking compound, 318.

The compartment 312 has a forward wall 320 forming an applicatorradiating surface 322, the wall being formed from a material such asglass which has a relatively high thermal conductivity, as compared toPlexiglas for example, and sealed to the waveguide 302 with anappropriate glue, or caulking compound, 324.

A pair of fittings 326 secured through a pair of holes 328 in thePlexiglas wall 316, and connected to tubing 330, enables a seconddielectric medium, or fluid, 332 to be pumped, or circulated, throughthe compartment, the second dielectric acting as a cooling medium forcooling the applicator radiating surface 324 and surface portions ofliving tissue, not shown, during radiation thereof when the tissue isheld against the applicator radiating surface.

Distilled water, which has a dielectric constant of approximately 70 to80, may be used as the fluid dielectric, 332. Although other fluiddielectric mediums may be used which may have a dielectric constant ofapproximately 20 to 100, distilled water is preferred because of itsavailability, cost, and ease in handling. It should be appreciated thatthe dielectric mediums 122 and 332 partially fill the waveguide 302which enables the waveguide applicator 300 to have a characteristicimpedance, over the frequency range of 200 to 800 MHz, of approximately50.

As was discussed in connection with FIG. 6, a coupler 212, including acoaxial type connector 158 mounted to top plate 340 of the centralchannel 304 is provided for receiving electromagnetic energy from thecable 22 and launching such energy into the waveguide applicator 300. Asdiscussed in connection with the applicator 190, a slot 342 may beprovided in the central channel top plate 340 to enable the adjustmentof the coupler 212 to optimize the position of the coupler within theridged waveguide applicator 300 in accordance with the procedurehereinbefore outlined.

A waveguide top plate 350 and bottom plate 352 are interconnected withthe central channel top plate 340 and a central channel bottom plate354, respectively, by upstanding walls 356, 358. This configurationenables the coupler 212 to be mounted directly onto the central channeltop plate 340 and further enables ready access to the rear compartmentwall 316 in order to facilitate attachment of the fittings 326 thereto.

As hereinabove discussed in connection with the applicator 190, thecoupler connector center portion 168, not shown in FIGS. 11 and 12, isextended by a rod, or pin, 220 into the dielectric medium 122. In orderto provide proper capacitive coupling between the launcher 210 and thewaveguide, a T bar section 222 is attached to the end of the pin 220.

It is important that the location of the launcher with respect to thedielectric medium 122 and an open portion 362 of the waveguide 302, isdetermined in a manner similar to that discussed in connection with theside loaded applicator 20, and the ridged applicator 190, in order toenable the waveguide applicator 300, to operate over the frequency rangeof 200 to 800 MHz, and at the same time, enable the waveguide to have anaverage characteristic impedance substantially equal to that of livingtissue, or simulations thereof.

A feature of the embodiment of the present invention as shown in FIGS.11 and 12 is the fact that the fluid dielectric 332 also acts as acollimator for electromagnetic energy radiated from the applicatorirradiating surface 322. Additionally, a larger radiation surface 322,may be provided, as compared with the radiating surface 211, of theapplicator 190, for irradiating a larger surface as may be desired forlarger malignant growths.

In order to achieve this collimating effect, the compartment 312, aswell as the fluid dielectric 332 must be contained within the waveguide302. The electromagnetic energy conducted by the dielectric 122 in thecentral channel 304, is coupled into the fluid dielectric 332 throughthe Plexiglas back plate 316, and is conducted, or propagated,throughout the fluid dielectric 332 and emitted from the radiatingsurface 322. The electromagnetic lines of force, not shown, areredistributed by the fluid dielectric 332, so as to spread throughoutthe fluid dielectric and across the radiating surface 332. The dominatemode of electromagnetic energy which propagates within the fluiddielectric is the TE₁,0 mode, as described, for example in, "ReferenceData for Radio Engineers", 5th Ed., Published by ITT, 1970.

Although the fluid dielectric 332 may be a lossy medium, only arelatively short length, compared to the length of the central channel304, is necessary to redistribute, or spread the electromagnetic energyto a greater area for emission from the radiating surface 322. Thelarger area enables a greater collimation of the emitted electromagneticenergy.

In general, as electromagnetic energy, radiated from a surface 368,(FIG. 13) penetrates a lossy medium, such as living tissue, divergence,in accordance with the well known formula 1/r², where r is the distancefrom the surface 368 does not occur until the radiated energy reaches acertain distance, B, from the radiating surface (FIG. 13). The areabeyond the distance B is known as the far field region 320, the areabetween the distance B and the radiating surface 368 being known as thenear field region 372.

In the near field region 372, the emitted electromagnetic energy, asrepresented by the lines 374 do not diverge significantly as they moveaway from the radiating surface 368 until they reach the distance B infront of the radiating surface. At that point the electromagneticenergy, as represented by the lines 376 begin to diverge in accordanceto the 1/r² formula. The divergence angle from the point B forward ofthe applicator is approximately θ_(a) where, θ_(a) is approximately##EQU3## τ_(m) being the wavelength of the radiated electromagneticenergy in tissue and a being a dimension of the radiation surface (FIG.13).

The boundary B, between the near field and the far field regions isknown to be approximately,

    B=A/2τ.sub.m

(where A=aperature area).

It is to be appreciated that electromagnetic energy beam divergence isdependent upon the area of the radiating surface 368, the onedimensional analysis described herein being chosen for clarity. As anexample, if characteristic dimensions of applicator 300 are 10 inchesdeep, 4 inches high, 5 inches wide with an internal dielectric channelof 1.5 inches high and 3 inches assuming the fluid chamber were removed,the radiating surface would be 1.5 by 3.0 inches. At a frequency of 433MHz, the wave length radiated into living tissue or simulations thereofis approximately 8.76 centimeters, which the boundary distance B, beingapproximately 0.65 inches, and the angle of divergence θ_(a) beingapproximately 148° in the vertical plane as shown in FIG. 13, and 74° ina perpendicular or horizontal plane, not shown.

Comparing now the increased radiating size of applicator 300, thecomparative dimensions is A equal to 4×5 inches, hence at 433 MHz, Bwould be approximately 2.9 inches with θ_(a) equal to approximately 50°,hence collimation is obtained to approximately 2.9 inches, or 7.4centimeters with a divergence angle of only approximately 50° beyondthis point.

Coupling of electromagnetic energy between the applicator 300 and livingtissue, not shown in FIGS. 11 and 12, may be further enhanced by meansof a pair of adjustable flaps 386, mounted to the waveguide 302 byhinges 388. The hinges enable the flaps to be moved in the directionsindicated by arrows 390, 392, so as to conform to tissue portions, notshown, which may extend beyond the waveguide forward end 314.

The flaps are preferably constructed of metallic substance 400, 402, andmay be flexible, to improve the efficiency of energy transfer into bodytissue, not shown.

A dielectric coating or medium 408 may be applied to the flaps 386 inorder to further enhance energy coupling, and prevent hot spoting. Itshould be appreciated that the applicator 300 may be constructed, inaccordance with this invention, in various sizes with the range ofradiated frequencies being lower as the dimensions of the applicator areincreased, or higher as the dimensions are decreased.

The effectiveness of the applicator 300 causing heating in simulated, orphantom tissue, by radiating electromagnetic energy thereinto atapproximately 800 MHz is shown in the FIGS. 14 and 15. Plotted in theseFigures is a set of isotherms showing the percent of change relative tothe greatest temperature change of 100% of an area radiated at a powerof approximately 50 watts with cooling dielectric fluid 332 flowingthrough the compartment 312 at approximately one gallon per minute. Thetemperature of the fluid dielectric was thermostatically controlled tobetween 5° and 10° centigrade.

FIG. 14 shows isotherms taken at a distance of 1 centimeter into theradiated phantom material, from the irradiating surface, and FIG. 15shows isotherms at a distance of 4 centimeters from the radiatingsurface. Isotherm lines are shown for various percentages, as indicatedon the drawings, of the maximum temperature achieved at the indicateddepth of 1 centimeter or 4 centimeters. Superimposed on the plots are anoutline 420 of the radiating surface 324 along with an outline 422 ofthe flaps 386.

Comparing FIGS. 14 and 15 with FIG. 10, it can be seen that the use ofthe fluid dielectric for spreading and collimating the emitted radiationis effective in causing a larger area, within the irradiated sample, tobe heated.

It is to be appreciated that the plots shown in FIGS. 14 and 15 arebased on experimental measurement, and that discontinuities andnipple-like variations therein, are attributed to experimental error.

Although there has been described above particular arrangements of anapparatus for irradiating living tissue, or simulations thereof, inaccordance with the invention for the purpose of illustrating the mannerin which the invention may be used to advantage, it will be appreciatedthat the invention is not limited thereto. Accordingly, any and allmodifications, variations or equivalent arrangements which may occur tothose skilled in the art, should be considered to be within the scope ofthe invention as defined in the appended claims.

What is claimed is:
 1. A system for irradiating living tissue, orsimulations thereof, comprising in combination:(a) an electromagneticradiation source having an output impedance equivalent to a firstimpedance of approximately 50 ohms over a selected frequency range, saidfrequency range having a bandwidth ratio in excess of 50% for providingvaried depth penetration of electromagnetic radiation in said livingtissues, or simulations thereof; (b) an applicator means adapted forirradiating electromagnetic energy into said tissue, said applicatormeans including a waveguide transmission line having electricallyconductive top, bottom and sidewalls and a radiation emitting face andan opposite rearward face, dielectric means disposed in the transmissionline for enabling the transmission line to have a characteristicimpedance when radiating electromagnetic energy into the tissue, orsimulations thereof, over the selected frequency range, equivalent tothe first impedance, said dielectric means further including adielectric portion having a dielectric constant of approximately 12 andhaving a forward surface spaced rearwardly of said transmission lineemitting face and having a rearward surface spaced forwardly from saidtransmission line rearward face, and coupling means connected to atransmission means external to the applicator means for receivingelectromagnetic energy from the transmission means and launching theelectromagnetic energy into the waveguide transmission line forirradiating thereby into tissue or simulations thereof, and means forcooling surface portions of the tissue, or simulations thereof, duringirradiation, said cooling means being disposed forwardly adjacent tosaid surface of said dielectric portions; (c) said transmission meansinterconnected between the electromagnetic radiation source and theapplicator means for transmitting electromagnetic energy therebetween,said transmission means having a characteristic impedance equivalent tosaid first impedance at the selected frequency; and (d) feedback controlmeans connected to said electromagnetic radiation source and includingelectromagnetically non-interfering temperature sensing means fordisposal at different locations in said living tissue, or simulationsthereof, for measuring temperature, said control means for controllingthe output of the electromagnetic radiation source in response tooutputs from the temperature sensing means.
 2. A system for irradiatingliving tissue, or simulations thereof, according to claim 1 wherein saidcooling means further includes a blower to provide a flow of air acrossthe surface of the tissue being irradiated.
 3. A system for irradiatingliving tissue, or simulations thereof, according to claim 2 wherein saidcontrol means further is provided for varying the electromagneticradiation source frequency in response to the temperature sensoroutputs.
 4. A system for irradiating living tissue, or simulationsthereof, according to claim 3 wherein said feedback control meansincludes monitor means to continuously provide output data relating toeach temperature sensor output and to the electromagnetic radiationsource frequency and power output.
 5. A system for irradiating livingtissue, or simulations thereof, according to claim 4 wherein saidfeedback control means further includes means to record said monitoroutput data.
 6. A system for irradiating living tissue, or simulationsthereof, according to claim 5 wherein said feedback control meansfurther includes display means to provide a visual display of saidmonitor output data.
 7. A system for irradiating living tissue, orsimulations thereof, according to claim 1 wherein said control meansfurther controls the cooling means in response to an output from onetemperature sensor located adjacent to the tissue surface.
 8. A systemfor irradiating living tissue, or simulations thereof for causinghyperthermia therein, comprising in combination:(a) an electromagneticradiation source having an output impedance equivalent to a firstimpedance of approximately 50 ohms over a selected frequency range, saidfrequency range having a bandwidth ratio in excess of 50% for providingvaried depth penetration of electromagnetic radiation in said livingtissues, or simulations thereof; (b) an applicator means adapted forirradiating electromagnetic energy into said tissue, said applicatormeans including:(i) a waveguide transmission line having an electricallyconductive top, bottom and sidewalls, in a radiation emitting face andfurther including a transmission line length; (ii) dielectric meansdisposed in the transmission line for enabling the transmission line tohave a characteristic impedance, when irradiating electromagnetic energyinto the tissue, or simulations thereof, within a preselected frequencywithin said frequency range and approximately matching the firstimpedance in said preselected frequency range, said dielectric meansincluding a portion extending rearwardly from said radiation emittingface towards the rearward face for a distance which is less than thetransmission line length; and (iii) coupling means for receiving saidelectromagnetic energy from a transmission means and for launching theelectromagnetic energy into the waveguide transmission line forirradiation thereby into tissue or simulations thereof, said couplingmeans including a radiation energy coupler disposed through one of saidtransmission line walls into said portion at an axial position adjacenta rearward end thereof; (c) said transmission means interconnectedbetween the electromagnetic radiation source and the applicator meansfor transmitting the electromagnetic energy therebetween, saidtransmission means including a characteristic impedance equivalent tosaid first impedance in the selected frequency range; and (d) feedbackcontrol means connected to said electromagnetic radiation source meansand further including an electromagnetically non-interfering temperaturesensing means for disposal at different locations in said living tissue,or simulations thereof for measuring temperature therein, said controlmeans for controlling the output of the electromagnetic radiation sourcein response to outputs from the temperature sensing means.
 9. A systemfor irradiating living tissue, or simulations thereof, for causinghyperthermia therein, comprising in combination:(a) an electromagneticradiation source having an output imepdance equivalent to a firstimpedance of approximately 50 ohms over a selected frequency range, saidfrequency range having a bandwidth ratio in excess of 50% for providingvaried depth penetration of electromagnetic radiation in said livingtissues, or simulations thereof; (b) an applicator means adapted forirradiating the electromagnetic energy into said tissue, said applicatormeans including:(i) a waveguide transmission line having electricallyconductive top, bottom and sidewalls and a radiation emitting face andan opposite rearward face; (ii) dielectric means disposed in thetransmission line for enabling the transmission line to have acharacteristic impedance, when radiating electromagnetic energy into thetissue, or simulations thereof, within the frequency range equivalent tothe first impedance in the frequency range, said dielectric meansfurther including a dielectric portion which has a forward surfacespaced rearwardly of said transmission line emitting face and which hasa rearward surface spaced forwardly from said transmission line rearwardface; (iii) coupling means configured for receiving said electromagneticenergy from a coaxial type conductor connected to the electromagneticradiation source and for launching the electromagnetic energy into thetransmission line for irradiation thereby into tissue or simulationsthereof; (iv) means for cooling surface portions of the tissue orsimulations thereof during irradiation, said cooling means beingdisposed forwardly adjacent to said surface of said dielectric portion;and (c) feedback control means connected to the electromagneticradiation source and including a electromagnetically non-interferingtemperature sensing means for disposal at different locations in saidliving tissue, or simulations thereof for sensing temperature therein,said control means for controlling the output of the electromagneticradiation source in response to the outputs from the temperature sensingmeans.
 10. A system for irradiating living tissue, or simulationsthereof, comprising, in combination:(a) a variable frequencyelectromagnetic radiation source having an output impedance equivalentto a first impedance of approximately 50 ohms over a selected frequencyrange having a bandwidth ratio in excess of 50% for providing varieddepth penetration of electromagnetic radiation in said living tissues,or simulations thereof; (b) an applicator means for radiatingelectromagnetic energy into the tissue and including a dielectric havinga dielectric constant approximately 12 to provide a characteristicimpedance when radiating electromagnetic energy into tissue, orsimulations thereof, equivalent to said first impedance throughout thefrequency range; (c) transmission means interconnected between theelectromagnetic radiation source and the applicator means fortransmitting electromagnetic energy therebetween, said transmissionmeans including a coax cable to provide a characteristic impedanceequivalent to said first impedance throughout the frequency range; and(d) feedback control means in operative relationship with saidelectromagnetic source and including an electromagneticallynon-interfering temperature sensing means for disposal in said livingtissue, or simulations thereof, for measuring temperature and includinga controller means connected to the electromagnetic radiation source forcontrolling the output of the electromagnetic radiation source inresponse to the output of the temperature sensing means.